The present invention relates generally to brake actuators and more specifically to a vibration isolation system for brake actuators used with caliper brakes.
Since the 1960's, rail car operation and engineering have been experiencing the need for faster, safer and more light weight trains. The industry has been gaining experience in metallurgy and failure mechanisms as well as the ability to generate better definition of vibration operating environments affecting the brake systems.
The need for faster, safer trains has dictated the use of more complicated brake actuator and caliper systems. These systems usually incorporate intricate slack adjustor systems. With so many more pieces, the probability of failure due to component systems responding to a wider spectrum of damaging vibrations has become a problem.
With the advancements in vibration technology has come a better understanding of the brake component failure mechanisms. The damaging shock and vibrations can be accurately defined. To isolate these from the brake caliper and actuator, a tuneable, adjustable, isolation system is needed which will reduce the shock loading also. The present systems are not easily adjusted without an expensive and time consuming design or production modification. Many brake systems do not have any shock or vibration isolation for the calipers or actuators.
Many suspension systems address shock but do not reduce one of the major causes of wear, fretting. Fretting is where a component is able to move or has play in it due to assembly tolerances. While the components are in the unloaded condition, namely brakes not applied, they are free to move around. In many cases, they rattle around or are responding to the ever present broad range of vibration generated by a rail car's steel wheel and stiff primary suspension systems. These never ending, continuous micro-motions are the main ingredient in fretting. Because the mating steel on steel surfaces are not heavily loaded when the brakes are not applied, moisture and oxygen can continually attack and form oxides on the mating surfaces. These continually forming oxides are then quickly removed by the fretting motions, to begin the cycle again.
Many brake systems with a shock absorbing mount between the caliper and actuator assembly require additional brackets and linkages to transmit the braking loads to the truck frame. These systems with their extra linkages and brackets are less compact and more complicated.
Many brake vibration isolation systems are not dedicated to the actuator alone. They may suspend the entire mechanism of calipers, levers, pads, pins and actuators. While the brake systems are not applied, the entire sub-system is free to vibrate within itself, causing offensive noises and possibly damaging resonant vibrations.
Thus, the object of the present invention is to provide a rattle free brake actuator mounting system.
Another object of the present invention is to provide an actuator vibration isolation system with reduced fretting corrosion of the actuator, caliper and pin system.
An even further object of the present invention is to provide an actuator system capable of fine tuning in the field.
A still further object of the present invention is to provide a brake actuator vibration isolation system which can be retrofitted to existing brake systems.
These and other objects are achieved by brake caliper and actuator assembly wherein a spring is provided between and separates an actuator and a lever of the caliper for retarding vibration of the actuator relative to the lever when the brake assembly is not actuated. An actuator pin, which connects the lever of the caliper to the actuator, includes a first threaded portion received in the caliper and separated by shoulder from a second non-threaded portion which is received in the actuator. A recess may be provided at the shoulder for receiving the spring. A locking plate is provided for locking the actuator pin to the lever.
The spring is a compressible ring about the actuator pin and between the actuator and the lever. The spring is preloaded by the actuator pin and a washer may be provided between the actuator and the spring to further adjust the preloading of the spring as well as to reduce the wear on the spring. Preferably, the spring is a ring of rigid non-metal material. A spring may also be a metal coil spring or a bevelled spring washer.
A method of designing a brake caliper and actuator assembly includes determining the anticipated vibration between the actuator and the lever when the brake caliper assembly is not actuated. The spring characteristics between and separating the actuator and the lever is selected to retard the anticipated vibration of the actuator relative to the lever when the brake caliper assembly is not actuated. Selecting includes selecting the preloading of the spring by the actuator pin. Preloading may be determined by selecting the thickness of a washer about the actuator pin and between the actuator pin and the actuator to vary the preloading of the spring. The selecting of the characteristics may also involve selecting material of the spring, its cross-section as well as other characteristics. The method also includes providing an actuator pin having a first threaded portion separated by shoulder from a second non-threaded portion and including a recess at the shoulder for receiving the spring.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.